it's not only about the relationship being over, it's merely about him realizing that they are happy on the one hand, but on the other they won't be for ever, because they are too different or whatsoever. so he leaves her, being completely unselfish, because he really does love her and wishes her the good life she deserves. at first, she's desperate because of his decision, so he tries to calm her down. and she makes it, she finds somebody and gets happy. and at this point, as he is only human, the selfish thoughts come back and he regrets to have lost her. but he doesn't regret his decision to leave her, i think. if anything, he regrets his decision to start the relationship in the first place.
it's not only about the relationship being over, it's merely about him realizing that they are happy on the one hand, but on the other they won't be for ever, because they are too different or whatsoever. so he leaves her, being completely unselfish, because he really does love her and wishes her the good life she deserves. at first, she's desperate because of his decision, so he tries to calm her down. and she makes it, she finds somebody and gets happy. and at this point, as he is only human, the selfish thoughts come back and he regrets to have lost her. but he doesn't regret his decision to leave her, i think. if anything, he regrets his decision to start the relationship in the first place.